The invention relates to a storage phosphor panel for radiography systems having a storage layer which is arranged on a support panel and whose image information, excited by a stimulation radiator, is radiated as information light radiation at another frequency.
In a conventional radiographic system an X ray radiograph is obtained by X rays transmitted image-wise through an object and converted into light of corresponding intensity in a so called intensifying screen (X ray conversion screen) wherein phosphor particles absorb the transmitted X rays and convert them into visible light and/or ultraviolet radiation to which a photographic film is more sensitive than to the direct impact of X rays.
According to another method of recording and reproducing an X ray pattern disclosed e.g. in U.S. Pat. No. 3,859,527 a special type of phosphor is used, known as a photostimulable phosphor, which being incorporated in a panel is exposed to incident patternwise modulated X rays and as a result thereof temporarily stores therein energy contained in the X ray radiation pattern. At some interval after the exposure, a beam of visible or infrared light scans the panel to stimulate the release of stored energy as light that is detected and converted to electrical signals which are processed to produce a visible image. For this purpose, the phosphor should store as much as possible of the incident X ray energy and emit as little as possible of the stored energy until stimulated the scanning beam. This is called xe2x80x9cdigital radiographyxe2x80x9d or xe2x80x9ccomputed radiographyxe2x80x9d.
During the scanning of storage phosphor panels with a stimulation laser, the area used for imaging is scanned line by line. In this case, the stimulation light can be focused relatively easily to the required pixel size, in which case the stimulation can be effected in spot form, in so called xe2x80x9cflying spot scannersxe2x80x9d, or in line form in a line CCD readout (charge coupled device). The actual image information, that is to say the emitted light, leaves the image panel in the form of light of a different wavelength. It can be demonstrated that, even with phosphors which are structured in needle form, the angular distribution of the emitted light is directed forwards only to a slightly greater extent than the light emanating from a diffusively scattering layer (Lambertian radiator).
When considering the signal chain, it is crucial that a second quantum bottleneck is not created at any point in the system. The collection efficiency of the light detector is particularly critical, since any intensity of the emitted signal that is lost here, e.g., as a result of mismatch, cannot be recovered at a later point.
The known storage phosphor panels have hitherto usually been scanned by a xe2x80x9cflying spotxe2x80x9d laser in spot form in the red spectral region. A single photomultiplier with an optical waveguide coupled to it collects the emitted light. With this geometry, owing to the spotlike nature of the emitting source, the optical waveguide can be matched very favourably to the Lambertian radiation characteristic.
With a new generation of storage panels with CCD read-out lines, however, this problem is difficult to solve. Particularly with a version in which stimulation and read-out take place at the same side, the larger distance of the CCD detector from the layer surface results in a reduced effective aperture and thus in a distinct reduction of the collecting efficiency. It has been disclosed to use microlenses in the reader for stimulated light of storage phosphor plates for focusing the emitted light onto the CCD. Such disclosures are found in e.g., in DE-A-1 97 52925 and in U.S. Pat. No. 5,208,459. In these disclosures, the microlenses are placed between the storage phosphor panel and the CCD""s, so that the reader still has to be larger than desired because it has to accommodate the lens systems between the storage plate the CCD. Thus means and ways to further reduce the dimensions of a reader for storage phosphor plates are still desired.
It is an object of the invention to provide a storage phosphor panel making it possible to reduce the dimensions of the reader needed to read (i.e. stimulate the plate and read the emitted light) the phosphor plate.
It is an object of the invention to provide a storage phosphor panel having a particularly high collecting efficiency irrespective of the operating mode in transmitted light operation or reflected light operation.
It is a further object of the invention to provide a storage phosphor panel with a particularly high collection efficiency when the reading of the stimulated light proceeds with a CCD-light detector.
Further advantages, features and details of the invention emerge from the following description of an exemplary embodiment and with reference to the drawings.
The objects of the invention are realised by providing a storage phosphor panel having a storage phosphor layer, characterised in that a focusing layer (8) which comprises a multiplicity of adjacent microlenses (9) is incorporated in said storage phosphor panel and forms an outer surface of said panel.
Preferably said storage phosphor panel comprises a support and the storage phosphor layer is present on said support and the multiplicity of adjacent microlenses (9) forms an outer surface of the panel at the phosphor layer side of the panel.